Phenolic resins for the wood industry have been refined for the past twenty years to the current "state of the art" and as such, perform to a well defined standard. The recent development of isocyanate-based adhesives has provided wood adhesives that are somewhat faster curing than phenolics and that are, in some cases, replacing phenolics due to their faster cure rates, even though they have some negative health and economic aspects.
However, phenol-formaldehyde resins remain widely used as adhesives and binders in many wood products, including wood products such as plywood, particleboard, fiberboard, hardboard and oriented strandboard. The productivity of most mills manufacturing wood products using liquid phenol-formaldehyde resole (PF) binders is limited by the cure speed of the binder in the hot press. This is because of the inherently slow thermal cure of these products, compared to other commonly used binders, and because of the need to eliminate moisture from the system during curing.
Several methods have been used to speed up the cure rate of PF resin binders.
There are the methods in which various kinds of alkali metal hydroxides, water-soluble alkali metal weak acid salts, or water-insoluble multivalent metal carbonates are added to the PF resin in order to accelerate its curing.
In order to speed up the cure rate (i.e, cut down the cure time), curing agents like alkylene carbonate have been utilized. U.S. Pat. No. 4,961,795 to Detlefsen et al describes such a curing agent. Unfortunately, mixing this type of curing agent with a phenol-formaldehyde resin usually results in a mixture that has a very limited "pot life" for process manipulation.
It was the intention of the inventors to develop an additive that will accelerate the curing of phenol-formaldehyde resin and provide a synergistic effect by improving bond quality of the manufactured wood products bonded with the resin. Further, it was the intention of the inventors that binder made by mixing the additive with the phenol-formaldehyde resin have a reasonable "pot life."